System design interview question

Design Snapchat (ephemeral content)

Medium · System design (HLD) · Company tags: Snap

The prompt

"Design Snapchat. Users send photos and short videos to friends. Once viewed, a snap disappears. Stories last 24 hours then vanish. 400 million daily users, 5 billion snaps a day."

What this round really tests

deletion as a first-class design goal. Every other system in this list is built to keep data. This one is built to destroy it — reliably, at 5 billion items a day, across caches, CDNs, replicas, and backups. Candidates who design Instagram and add a DELETE at the end have missed the question.

Clarifying questions worth asking

Does "disappear" mean truly deleted from storage?
Can recipients screenshot?
Group snaps / stories?
Do we store anything after viewing?
Offline recipients?
Encryption?

How the round usually runs

0–5 min: Scoping
5–10 min: Estimates
10–18 min: Architecture
18–30 min: Deep dive
30–38 min: Deep dive
38–45 min: Wrap

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